Optical characteristic measurement system and calibration method for optical characteristic measurement system

ABSTRACT

There is provided an optical characteristic measurement system that can be set up in a relatively short time and can increase a detection sensitivity. The optical characteristic measurement system includes a first measurement apparatus. The first measurement apparatus includes: a first detection element arranged in a housing; a first cooling unit at least partially joined to the first detection element that cools the detection element; and a suppression mechanism that suppresses temperature variations occurring around the detection element in the housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 15/200,535filed Jul. 1, 2016 and claims priority to Japanese Patent ApplicationNo. 2015-136036 filed Jul. 7, 2015, the disclosure of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present technique relates to an optical characteristic measurementsystem that can measure optical characteristics, and a calibrationmethod for the optical characteristic measurement system.

Description of the Background Art

There is a need for measuring the feeble light emitted by aphotosensitizing substance in order to evaluate characteristics of amaterial or a reagent including the substance. For example, JapanesePatent Laying-Open No. 09-159604 discloses a singlet oxygen measurementapparatus that can measure even a sample including a photosensitizingsubstance having a light absorption characteristic with respect to anarbitrary wavelength in a range of an ultraviolet region to a visibleregion, and a sample that is directly and indirectly unstable withrespect to the light and available only in a small amount.

In addition, Japanese Patent Laying-Open No. 09-292281, InternationalPublication No. 2010/084566 and Japanese Patent Laying-Open No.2011-196735 disclose a measurement apparatus and a measurement methodfor measuring the quantum efficiency indicating a ratio between anamount of photons absorbed by a sample including a fluorescent substanceand an amount of photons of fluorescence generated from the sample.

In the singlet oxygen measurement apparatus disclosed in Japanese PatentLaying-Open No. 09-159604, a liquid nitrogen cooling-type germaniumdetector is used to increase a detection sensitivity. By cooling adetection element with liquid nitrogen or the like, the detectionelement can be stabilized and a detection dynamic range can be enlarged.On the other hand, in order to cool the detection element with liquidnitrogen, a few hours preparation including precooling and the like isrequired before the actually usable state is achieved, and thus, thissinglet oxygen measurement apparatus is not practical.

SUMMARY OF THE INVENTION

There is a demand for realizing an optical characteristic measurementsystem that can be set up in a relatively short time and can increase adetection sensitivity.

According to an aspect of the present invention, there is provided anoptical characteristic measurement system including a first measurementapparatus. The first measurement apparatus includes: a first detectionelement arranged in a housing; a first cooling unit at least partiallyjoined to the first detection element, for cooling the first detectionelement; and a suppression mechanism for suppressing temperaturevariations occurring around the first detection element in the housing.

Preferably, the suppression mechanism includes a second cooling unit atleast partially joined to the housing, for transferring heat in thehousing to outside the housing.

Preferably, the suppression mechanism includes a heat insulationmechanism arranged around the housing, for reducing heat entry into thehousing from around the housing.

Preferably, the optical characteristic measurement system furtherincludes a second measurement apparatus. The first measurement apparatusfurther includes a first diffraction grating arranged to correspond tothe first detection element and configured to guide light in a firstwavelength range to the first detection element. The second measurementapparatus includes: a second detection element arranged in a housing;and a second diffraction grating arranged to correspond to the seconddetection element and configured to guide light in a second wavelengthrange to the second detection element. The first detection element ofthe first measurement apparatus is configured to have a detectionsensitivity higher than a detection sensitivity of the second detectionelement of the second measurement apparatus.

Preferably, the optical characteristic measurement system furtherincludes a bifurcated fiber for bifurcating the light from an object tobe measured and guiding the light to each of the first and secondmeasurement apparatuses.

Preferably, the first measurement apparatus is configured to have thedetection sensitivity to a wavelength component in a near-infraredregion. The second measurement apparatus is configured to have thedetection sensitivity to at least a part of wavelength componentsincluded in a range of an ultraviolet region to a visible region.

According to another aspect of the present invention, there is provideda calibration method for an optical characteristic measurement systemincluding a first measurement apparatus and a second measurementapparatus configured to have a detection sensitivity lower than adetection sensitivity of the first measurement apparatus. Thecalibration method for the optical characteristic measurement systemincludes: arranging a light source preliminarily valued by an energyvalue and the second measurement apparatus in accordance with a firstarrangement condition, and determining an energy calibration coefficientof the second measurement apparatus based on an output value obtained byreceiving light from the light source at the second measurementapparatus; arranging the light source and the second measurementapparatus in accordance with a second arrangement condition, anddetermining a converted energy value of the light source correspondingto the second arrangement condition based on the output value obtainedby receiving the light from the light source at the second measurementapparatus and the energy calibration coefficient of the secondmeasurement apparatus; and arranging the light source and the firstmeasurement apparatus in accordance with the second arrangementcondition, and determining an energy calibration coefficient of thefirst measurement apparatus based on an output value obtained byreceiving the light from the light source at the first measurementapparatus and the converted energy value of the light sourcecorresponding to the second arrangement condition.

According to an embodiment of the present invention, there is providedan optical characteristic measurement system that can be set up in arelatively short time and can increase a detection sensitivity.

In addition, according to an embodiment of the present invention, thereis provided a calibration method for an optical characteristicmeasurement system including a first measurement apparatus and a secondmeasurement apparatus configured to have a detection sensitivity lowerthan a detection sensitivity of the first measurement apparatus.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a configuration example of an opticalcharacteristic measurement system including an optical characteristicmeasurement apparatus according to the present embodiment.

FIGS. 2A and 2B are diagrams for describing a method for measuringoptical characteristics with the optical characteristic measurementsystem shown in FIG. 1.

FIG. 3 is a schematic view showing an apparatus configuration of a dataprocessing apparatus forming the optical characteristic measurementsystem shown in FIG. 1.

FIG. 4 is a schematic view showing an apparatus configuration of themeasurement apparatus forming the optical characteristic measurementsystem shown in FIG. 1.

FIG. 5 is a graph showing a result of evaluation of an influence of atemperature drift in the measurement apparatus shown in FIG. 4.

FIG. 6 is a schematic view showing a main portion of an apparatusconfiguration of an optical characteristic measurement system suitablefor measurement of the quantum efficiency.

FIG. 7 is a flowchart showing a procedure of the measurement method withthe measurement apparatus according to the present embodiment.

FIGS. 8A and 8B are diagrams showing an example of a measurement resultwhen singlet oxygen is generated from fullerene (C₆₀) in a solvent withthe optical characteristic measurement system shown in FIG. 6.

FIG. 9 is a flowchart showing a procedure for performing calibration onthe optical characteristic measurement system according to the presentembodiment.

FIGS. 10A to 10C are schematic views for describing a procedure forperforming calibration on the optical characteristic measurement systemaccording to the present embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described in detail withreference to the drawings. In the drawings, the same or correspondingportions are denoted by the same reference characters, and descriptionthereof will not be repeated.

A. System Configuration Example

First, an optical characteristic measurement system 1 including anoptical characteristic measurement apparatus (hereinafter alsoabbreviated as “measurement apparatus”) according to the presentembodiment will be described. FIG. 1 is a schematic view showing aconfiguration example of optical characteristic measurement system 1including the optical characteristic measurement apparatus according tothe present embodiment.

Referring to FIG. 1, optical characteristic measurement system 1includes a light source 4, an integrator 6, a system main body 2 thathouses a measurement apparatus 100, and a data processing apparatus 200.Although FIG. 1 shows the configuration example in which light source 4,integrator 6 and measurement apparatus 100 are housed in a singlehousing, the present invention is not limited thereto. A part of thecomponents may be configured as a separate apparatus. In this case, onlyone or a plurality of measurement apparatuses 100 may form the opticalcharacteristic measurement system.

Optical characteristic measurement system 1 shown in FIG. 1 can measurevarious optical characteristics. Examples of the optical characteristicsinclude a total amount of light flux, an illuminance (or spectralirradiance), a brightness (or spectral radiance), a light intensity,color rendering (a chromaticity coordinate, an excitation purity, acorrelated color temperature, and color rendering properties), anabsorptivity, a transmittance, a reflectance, an emission spectrum (anda peak wavelength and a half-wave value), an excitation spectrum,external quantum efficiency (or external quantum yield), internalquantum efficiency (or internal quantum yield) and the like.

In the following description, the case of applying the excitation lightof a prescribed wavelength (typically, the light in a range of theultraviolet region to the visible region) to a sample including afluorescent substance, and detecting the fluorescence (typically, thelight in a range of the near-infrared region to the infrared region)generated from the sample will be illustrated by way of example. In thiscase, the optical characteristics to be measured typically include aspectrum and the quantum efficiency of the fluorescence generated fromthe sample.

Light source 4 generates the excitation light applied to the sample. Axenon discharge lamp (Xe lamp), a laser diode, a white LED (LightEmitting Diode) or the like is, for example, used as light source 4. Inthe case of measuring the quantum efficiency of the sample, themonochromatic light having a single wavelength corresponding to thecharacteristics of the sample is preferably used as the excitationlight. In the case where the generated excitation light has an extent inthe wavelength band (e.g., in the case of using a white light sourcesuch as a xenon discharge lamp), a wavelength band transmission filterfor selecting the target monochromatic light may be provided.

In optical characteristic measurement system 1, a hemisphericintegrating sphere is used as integrator 6. A spherical integratingsphere may also be used as integrator 6. By using the hemisphericintegrating sphere, the measurement accuracy can be increased and thesample can be attached and detached more easily.

FIG. 2A shows one example of a measurement method in the case ofmeasuring a powder sample or a solid sample, and FIG. 2B shows oneexample of a measurement method in the case of measuring a solutionsample.

Referring to FIG. 2A, integrator 6 forms a hemispheric integration spacetherein. More specifically, integrator 6 includes a hemispheric portion61 and a disc-shaped plane mirror 62 arranged to pass through asubstantial curvature center of hemispheric portion 61 and close anopening of hemispheric portion 61. An inner surface (inner wall) ofhemispheric portion 61 is provided with a light diffuse reflection layer61 a. Light diffuse reflection layer 61 a is typically formed byapplying or spraying a light diffusion material such as barium sulfateor PTFE (polytetrafluoroethylene). On the inner surface side ofhemispheric portion 61, plane mirror 62 has a mirror-reflecting(regular-reflecting and diffuse-reflecting) light diffuse reflectionlayer 62 a. Since light diffuse reflection layer 62 a of plane mirror 62is arranged to face the inside of hemispheric portion 61, a virtualimage of hemispheric portion 61 is formed. By combining the space (realimage) defined within hemispheric portion 61 and the virtual imageformed by plane mirror 62, the same illuminance distribution as anilluminance distribution in the case of using the spherical integratorcan be obtained.

A sample SMP1, which is a powder sample or a solid sample, is attachedto a sample window 65 formed in a region including the apex ofhemispheric portion 61. Sample SMP1 is attached to sample window 65 suchthat a fluorescent substance thereof is exposed to the inside ofhemispheric portion 61.

The excitation light generated from light source 4 propagates through anoptical fiber 5, passes through a light projecting optical system 50,and is applied to sample SMP1 arranged in integrator 6. Light projectingoptical system 50 includes a collective lens 52 and collects theexcitation light from light source 4 on sample SMP1. A light projectingwindow 64 for guiding the excitation light into integrator 6 is formedin plane mirror 62.

The light (typically, the fluorescence) generated from sample SMP1having received the excitation light is repeatedly reflected insideintegrator 6, and thus, the illuminance appearing on the inner surfaceof integrator 6 becomes uniform.

An observation window 67 for observing the illuminance on the innersurface of integrator 6 is formed in plane mirror 62, and a lightextraction portion 68 is provided to correspond to observation window67. An end of an optical fiber 7 optically connected to measurementapparatus 100 is connected to light extraction portion 68. Namely, thelight having an intensity corresponding to the illuminance on the innersurface (corresponding to a range of a field of view when seen fromobservation window 67) of integrator 6 enters measurement apparatus 100.Based on the light observed through optical fiber 7, measurementapparatus 100 measures the optical characteristics of sample SMP1 andthe like.

As shown in FIG. 2A, the user may simply attach sample SMP1 to samplewindow 65 provided at the apex (the lowermost portion in the figure) ofhemispheric portion 61, and thus, the work for attaching and replacingthe sample can be simplified even when measurement of a plurality ofsamples SMP1 is required.

Referring to FIG. 2B, in the case of measuring a sample SMP2 which is asolution sample, a sample holder 63 is attached to a sample window 66formed in a central portion of plane mirror 62, and sample SMP2 isarranged in sample holder 63. At this time, a standard reflection member69 is attached to sample window 65 formed in a region including the apexof hemispheric portion 61.

Light projecting optical system 50 is arranged at a position ofextension of sample holder 63 in the length direction so as tocorrespond to sample window 66. Light projecting optical system 50applies the excitation light from light source 4 to sample SMP2 throughthe inside of sample holder 63. The light (typically, the fluorescence)generated from sample SMP2 having received the excitation light isrepeatedly reflected in integrator 6, and thus, the illuminanceappearing on the inner surface of integrator 6 becomes uniform. Based onthe light observed through optical fiber 7, measurement apparatus 100measures the optical characteristics of sample SMP2 and the like withthe method similar to the method in FIG. 2A.

In the use state shown in FIG. 2B, a standard reflection member is alsoattached to light projecting window 64 (not shown, refer to FIG. 2A).

Depending on a material, characteristics or the like of the sample, there-excitation fluorescence may occur. The re-excitation fluorescence isa phenomenon in which the excitation light reflected by the surface ofthe sample is diffused and reflected in integrator 6, and thereafter,enters the sample again and further light emission occurs. In opticalcharacteristic measurement system 1, an error caused by suchre-excitation fluorescence can also be corrected.

Referring again to FIG. 1, measurement apparatus 100 receives the lightobserved through optical fiber 7, and outputs a measurement result (suchas a spectrum). Data processing apparatus 200 processes the measurementresult from measurement apparatus 100 to calculate the opticalcharacteristics of the sample. The details of measurement apparatus 100will be described below.

Data processing apparatus 200 is typically implemented by ageneral-purpose computer. FIG. 3 is a schematic view showing anapparatus configuration of data processing apparatus 200 forming opticalcharacteristic measurement system 1 shown in FIG. 1. Data processingapparatus 200 includes a CPU (Central Processing Unit) 202 for executingvarious programs including the operating system (OS), a main memory 204for temporarily storing data necessary for execution of the programs byCPU 202, and a hard disk 206 for storing in a non-volatile manner ameasurement program 208 executed by CPU 202. The components formingmeasurement apparatus 100 are connected by a bus 220 so as to allowmutual communication.

Measurement program 208 for implementing the measurement methodaccording to the present embodiment is prestored in hard disk 206. Suchmeasurement program 208 is read by a CD-ROM (Compact Disk-Read OnlyMemory) drive 210 from a CD-ROM 212 or the like which is one example ofa recording medium. Namely, measurement program 208 for implementing themeasurement method according to the present embodiment is stored in therecording medium or the like such as CD-ROM 212 and is distributed.Alternatively, measurement program 208 may be distributed via thenetwork. In such a case, measurement program 208 is received via anetwork interface 214 of data processing apparatus 200 and is stored inhard disk 206.

A display 216 shows the measurement result and the like to the user. Aninput unit 218 typically includes a keyboard, a mouse and the like, andaccepts the user's operation.

A part or all of the functions described above may be implemented by adedicated hardware circuit. In addition, data processing apparatus 200may be incorporated as a part of system main body 2.

B. Discovery of New Problem

The case of applying the excitation light having a wavelength componentin the ultraviolet region or the visible region to the sample andmeasuring the light generated from the sample is assumed, for example.In such measurement, the light generated from the sample is in manycases the very feeble light having a wavelength component in a range ofthe near-infrared region to the infrared region. In addition, thelifetime of some samples is short and thus only a small amount ofmeasurement time can be secured.

Therefore, the use of a measurement apparatus having a highest possibledetection sensitivity is preferable. There is also known a method forincreasing the detection sensitivity by cooling the detection elementwith liquid nitrogen and the like as in the prior art. However, thismethod has such a problem that it takes a long time to perform a setupand handling is not easy.

Thus, by realizing the measurement apparatus with a detection elementthat can be used at an ordinary temperature without special cooling withliquid nitrogen and the like, the convenience of measurement isenhanced. In order to avoid a temperature-induced disturbance, theaforementioned detection element used at an ordinary temperature isprovided with a function for keeping the temperature of the detectionelement itself constant.

The inventors of the present application have found such a new problemthat when a detection gain of the detection element is increased inorder to detect the very feeble light, measurement is affected by theambient temperature of the measurement apparatus although thetemperature of the detection element itself is kept constant. As aresult of earnest study, the inventors of the present application havereached a conclusion that with variations in ambient temperature of themeasurement apparatus, temperature variations occur in the measurementapparatus as well and the detection element having an increased gainalso captures variations in radiant heat caused by the temperaturevariations, and as a result, the measurement result has an error causedby the variations although the intensity of light to be measured doesnot vary. Thus, the inventors of the present application have inventedmeasurement apparatus 100 in which a function not causing the influenceof the temperature variations occurring in the measurement apparatus,i.e., the influence of the radiant heat is newly adopted in addition tothe detection element itself. In measurement apparatus 100 according tothe present embodiment, stable measurement is possible even when theambient temperature of measurement apparatus 100 varies.

C. Configuration Example of Measurement Apparatus 100

Next, a configuration example of measurement apparatus 100 according tothe present embodiment will be described.

FIG. 4 is a schematic view showing an apparatus configuration ofmeasurement apparatus 100 forming optical characteristic measurementsystem 1 shown in FIG. 1. Referring to FIG. 4, measurement apparatus 100is a spectral photodetector, and includes an optical slit 104, a concavediffraction grating 106 and a detection element 108. These componentsare arranged in a housing 102.

A part of housing 102 is provided with a connection member 116 forattaching the end of optical fiber 7. By connection member 116, anoptical axis at an opening end of optical fiber 7 is aligned with acentral axis of optical slit 104. The light (hereinafter also referredto as “light to be measured”) extracted from integrator 6 propagatesthrough optical fiber 7 and passes through optical slit 104 ofmeasurement apparatus 100. A cross-sectional diameter of the light to bemeasured is adjusted in optical slit 104 and the light to be measuredenters concave diffraction grating 106.

The light to be measured enters concave diffraction grating 106, andthereby, the respective wavelength components included in the light tobe measured are optically separated. Namely, the light to be measured isdiffracted by concave diffraction grating 106, and thereby, therespective wavelength components included in the light to be measuredtravel in different directions corresponding to the wavelengths of therespective wavelength components. The respective wavelength componentsenter detection element 108 optically aligned with concave diffractiongrating 106. Concave diffraction grating 106 is arranged to correspondto detection element 108 and is configured to guide the light in aprescribed wavelength range (the near-infrared region to the infraredregion in this configuration example) to detection element 108.

An array sensor formed by arranging a plurality of independent detectionsurfaces side by side is used as detection element 108. A CCD(Charge-Coupled Device) image sensor may be used as detection element108. The number and length of the detection surfaces forming detectionelement 108 are designed depending on the diffraction characteristics ofconcave diffraction grating 106 and the wavelength width to be detected.For every prescribed wavelength width, detection element 108 which is anarray sensor detects an intensity spectrum of the light to be measured.

Detection element 108 has a self-cooling function at least partiallyjoined to detection element 108, for cooling detection element 108.Detection element 108 is a self-cooling type detection element and isconfigured to increase the detection sensitivity and increase an S/N(Signal to Noise) ratio by reducing thermal noise and reducing a darkcurrent. Specifically, detection element 108 has a base 110 having acooling function. The function for cooling detection element 108 ismounted in base 110. Typically, an electronic cooling element 111 suchas a Peltier element may be provided in base 110.

A cooling fin 112 is joined to a side of base 110 opposite to detectionelement 108, with a joining layer 113 interposed therebetween. A part ofthe heat generated at detection element 108 is absorbed by electroniccooling element 111 in base 110, and another part is transferred fromcooling fin 112 to outside measurement apparatus 100 through base 110and joining layer 113.

In electronic cooling element 111 of base 110, a current value and thelike are controlled by a cooling controller 114. Based on a detectionvalue from a not-shown temperature sensor and the like, coolingcontroller 114 controls the current value and the like such that thetemperature of detection element 108 is maintained at a predeterminedtemperature.

In addition to the function for cooling detection element 108 itself,measurement apparatus 100 according to the present embodiment hasmounted therein the function that does not have an influence of thevariations in radiant heat on detection element 108. Namely, measurementapparatus 100 has a function and configuration for suppressingtemperature variations occurring around detection element 108 in housing102. In the configuration example shown in FIG. 4, a temperature controlfunction for keeping the temperature of the internal space of housing102 constant and a heat insulation function for reducing the heat entryinto housing 102 are combined.

The temperature control function is implemented by a cooling mechanismat least partially joined to housing 102, for transferring the heat inhousing 102 to outside housing 102. More specifically, the temperaturecontrol function includes an electronic cooling element 130 arranged ona side surface of housing 102, and a heat dissipation plate 132 joinedto electronic cooling element 130. Electronic cooling element 130 isformed of a Peltier element or the like, and a current value and thelike are controlled by a cooling controller 134.

A flow path (not shown) through which a coolant (typically such as wateror chlorofluorocarbon) flows is formed within heat dissipation plate132. Heat dissipation plate 132 is coupled to a coolant circulation pump136 through coolant paths 138 and 139. Coolant circulation pump 136allows the coolant to circulate through coolant path 138, heatdissipation plate 132 and coolant path 139 in this order. When coolantcirculation pump 136 is operated, a part of the heat in housing 102 istransferred through heat dissipation plate 132 to outside, and inaddition, is thermally exchanged with the coolant at heat dissipationplate 132 and transferred to outside on the circulation path by coolantcirculation pump 136. Namely, heat dissipation plate 132 and coolantcirculation pump 136 promote cooling of the inside of housing 102 byelectronic cooling element 130.

The configuration of allowing the coolant to circulate between coolantcirculation pump 136 and heat dissipation plate 132 by coolantcirculation pump 136 has been described by way of example as thetemperature control function. However, instead of heat dissipation plate132, the configuration with the cooling fin may be employed similarly tothe self-cooling function of detection element 108.

The heat insulation function is implemented by a structure arrangedaround housing 102, for reducing the heat entry into housing 102 fromaround housing 102. More specifically, as the heat insulation function,a heat insulation member 120 is arranged on an outer perimeter ofhousing 102. Although a member made of an arbitrary material can be usedas heat insulation member 120, a fiber-based heat insulation member suchas glass wool and rock wool may, for example, be used. Alternatively, afoamed heat insulation member such as urethane foam and polystyrene foammay be used. By arranging such heat insulation member 120 on the outerperimeter of housing 102, the heat entry into housing 102 from aroundhousing 102 can be reduced.

As described above, measurement apparatus 100 according to the presentembodiment has the function and configuration that do not have aninfluence of the variations in radiant heat by suppressing thetemperature variations occurring around detection element 108. As longas the temperature variations occurring around detection element 108 issuppressed, measurement apparatus 100 is not limited to theconfiguration example shown in FIG. 4 and any configurations may beused.

For example, FIG. 4 shows the configuration example including thecombination of the temperature control function implemented mainly byelectronic cooling element 130 and the heat insulation functionimplemented mainly by heat insulation member 120. However, only one ofthese functions may be used.

As another configuration example, instead of heat insulation member 120,a vacuum layer may be provided on the outer perimeter side or on theinner perimeter side of housing 102 to reduce the heat entry from aroundhousing 102. Alternatively, a temperature-controlled coolant (typicallysuch as dry air and nitrogen) may be circulated around housing 102 tokeep the temperature in housing 102 constant.

Furthermore, two or more functions, of the plurality of functionsdescribed above, may be combined appropriately.

Based on the aforementioned new discovery by the inventors of thepresent application, in measurement apparatus 100 according to thepresent embodiment, the temperature in housing 102 having detectionelement 108 arranged therein is controlled and stabilized, and thus, theinfluence of radiant heat on detection element 108 can be reduced, thedetection sensitivity can be increased, and the S/N ratio can beincreased.

In addition to the function and configuration for suppressing thetemperature variations occurring around detection element 108 in housing102, a region that is not used for measurement, of the detectionsurfaces of detection element 108, may also be subjected to masking toincrease the stability of dark output.

D. Improvement Effect

Next, an improvement effect of a temperature drift in measurementapparatus 100 shown in FIG. 4 will be described. FIG. 5 is a graphshowing a result of evaluation of an influence of the temperature driftin measurement apparatus 100 shown in FIG. 4. FIG. 5 shows a result ofevaluation of variations in output value when measurement apparatus 100shown in FIG. 4 is arranged in a thermostat bath and the ambienttemperature is varied, and a result of evaluation of variations inoutput value when a measurement apparatus (Comparative Example) notincluding the temperature control function (electronic cooling element130, heat dissipation plate 132, cooling controller 134, and coolantcirculation pump 136) and the heat insulation function (heat insulationmember 120) shown in FIG. 4 is arranged in the thermostat bath and theambient temperature is varied.

“Ambient temperature” shown in FIG. 5 refers to temperature variationsin the thermostat bath. Specifically, the ambient temperature was variedby 5° C. within the range of 10° C. to 30° C. in a stepwise manner every2 hours.

As for the measurement apparatus of Comparative Example, measurement wasperformed in two types of states, i.e., in a state where the detectionsensitivity of the detection element was set to be standard (“(1)standard sensitivity (Comparative Example)” in FIG. 5) and in a statewhere the detection sensitivity of the detection element was set to behigher (“(2) higher sensitivity (Comparative Example)” in FIG. 5). Onthe other hand, as for measurement apparatus 100 shown in FIG. 4,measurement was performed in a state where the detection sensitivity ofthe detection element was set to be higher (“(3) higher sensitivity(present embodiment)” in FIG. 5).

In either case, the output value after dark correction, with theincidence of the light to be measured being shut off, is shown. Eachoutput value is a summed value obtained by repeating captures with anexposure time of 20 seconds four times. The measurement result shown inFIG. 5 is the output value after dark correction and a smaller value ismore preferable.

As shown in FIG. 5, it can be seen that even the measurement apparatusof Comparative Example is affected a little by the variations in ambienttemperature when the measurement apparatus of Comparative Example isused at the standard sensitivity. However, it can be seen that when thedetection sensitivity is increased, the measurement apparatus ofComparative Example is affected by the variations in ambient temperatureand the output value thereof varies even under the same measurementconditions.

In contrast, measures to reduce the heat entry into housing 102 fromaround housing 102 are taken in measurement apparatus 100 according tothe present embodiment, and thus, measurement apparatus 100 according tothe present embodiment is affected a little by the variations in ambienttemperature, although the detection sensitivity is set to be higher. Asa result, it can be seen that an influence of noise can be reduced ascompared with the case of using the measurement apparatus of ComparativeExample at the standard sensitivity.

E. Configuration Suitable for Measurement of Quantum Efficiency

Next, a configuration example suitable for measurement of the quantumefficiency will be described. For example, in the case of measuring thequantum efficiency of a sample including a fluorescent substance, it isnecessary to apply the excitation light having a wavelength component inthe ultraviolet region or the visible region to the sample, measure theapplied excitation light, and in addition, measure the fluorescencehaving a wavelength component in the near-infrared region or theinfrared region generated from the sample. Generally, the generatedfluorescence is very feeble as compared with the excitation light.Furthermore, the lifetime of some samples is short and thus only a smallamount of measurement time can be secured.

In such a case, a configuration including a combination of a firstmeasurement apparatus for measuring mainly the excitation light and asecond measurement apparatus for measuring mainly the fluorescence maybe used. An apparatus configuration suitable for measurement of thequantum efficiency of the fluorescent substance will be described belowby way of example.

FIG. 6 is a schematic view showing a main portion of an apparatusconfiguration of an optical characteristic measurement system 1Asuitable for measurement of the quantum efficiency. Referring to FIG. 6,optical characteristic measurement system 1A includes a measurementapparatus 100A for measuring mainly the excitation light, andmeasurement apparatus 100 for measuring mainly the fluorescence.

Optical characteristic measurement system 1A includes a bifurcated fiberfor bifurcating the light from an object to be measured and guiding thelight to each of measurement apparatus 100 and measurement apparatus100A. Namely, at a bifurcation portion 73, optical fiber 7 connected tolight extraction portion 68 of integrator 6 bifurcates into an opticalfiber 71 connected to measurement apparatus 100A and an optical fiber 72connected to measurement apparatus 100. Namely, the light observedthrough optical fiber 7 is divided into two lights and the two lightsenter measurement apparatus 100 and measurement apparatus 100A,respectively.

Measurement apparatus 100A is for measuring mainly the excitation lightand is designed such that a detection range is from the ultravioletregion to the visible region. On the other hand, measurement apparatus100 is for measuring mainly the fluorescence and is designed such that adetection range is from the near-infrared region to the infrared region.Namely, measurement apparatus 100 is mainly configured to have adetection sensitivity to a wavelength component in the near-infraredregion or the infrared region, and measurement apparatus 100A isconfigured to have a detection sensitivity to at least a part ofwavelength components included in the range of the ultraviolet region tothe visible region.

The apparatus configuration of measurement apparatus 100 is similar tothe above-described apparatus configuration shown in FIG. 4. On theother hand, the apparatus configuration similar to the above-describedapparatus configuration shown in FIG. 4 may be used as the apparatusconfiguration of measurement apparatus 100A. However, in the case ofmeasuring the excitation light, the intensity of the light to bedetected is higher, and thus, the temperature control function(electronic cooling element 130, heat dissipation plate 132, coolingcontroller 134, and coolant circulation pump 136) and the heatinsulation function shown in FIG. 4 do not necessarily need to beprovided. In optical characteristic measurement system 1A shown in FIG.6, measurement apparatus 100A not including the temperature controlfunction and the heat insulation function is used.

Because of the difference in detection range between measurementapparatus 100 and measurement apparatus 100A, concave diffractiongrating 106 of measurement apparatus 100 is configured to guide thelight in a prescribed wavelength range (the near-infrared region to theinfrared region in this configuration example) to detection element 108,while concave diffraction grating 106 of measurement apparatus 100A isconfigured to guide the light in a different wavelength range (theultraviolet region to the visible region in this configuration example)to detection element 108.

In addition, the detection sensitivity of detection element 108 ofmeasurement apparatus 100 is set to be higher than the detectionsensitivity of detection element 108 of measurement apparatus 100A. Inother words, measurement apparatus 100A is configured to have thedetection sensitivity lower than the detection sensitivity ofmeasurement apparatus 100.

According to optical characteristic measurement system 1A shown in FIG.6, the two measurement apparatuses can perform measurement in parallel,and thus, the spectrum in the range of the ultraviolet region to thenear-infrared region (or the infrared region) can be measuredsimultaneously. For example, as a function for measuring the spectrumfrom the ultraviolet region to the near-infrared region (or the infraredregion) with any measurement apparatus, there is known a configurationof mechanically rotating a diffraction grating sequentially tosequentially change a wavelength to be detected (i.e., sweep thewavelength). However, when such a function is used, there is a problemthat it takes a relatively long time to complete the measurement of thetarget spectrum. There is also a problem that at the time of shift tothe measurement in the near-infrared region or the infrared region aftercompletion of the measurement in the ultraviolet region and the visibleregion, the mechanical switching operation is required, which may causethe measurement instability.

In order to deal with these problems, optical characteristic measurementsystem 1A shown in FIG. 6 has an array sensor (detection element 108 ofmeasurement apparatus 100A) that can measure wavelengths in the range ofthe ultraviolet region to the visible region at a time, and an arraysensor (detection element 108 of measurement apparatus 100) that canmeasure wavelengths in the range of the near-infrared region to theinfrared region at a time. With such a configuration, the spectrum overthe wide wavelength range can be measured simultaneously and in a shorttime, without sweeping the wavelength. In addition, by optimizing thedetection sensitivity of detection element 108 of measurement apparatus100A for measuring the excitation light having a high emission intensityand the detection sensitivity of detection element 108 of measurementapparatus 100 for measuring the fluorescence having a low emissionintensity, it is possible to realize reasonable and economical opticalcharacteristic measurement system 1A that can measure the quantumefficiency with a high degree of accuracy.

F. Measurement Method

Next, a measurement method with measurement apparatus 100 shown in FIG.4 will be described. Similarly to optical characteristic measurementsystem 1A shown in FIG. 6, measurement can also be performed inaccordance with the similar procedure in the case of using measurementapparatus 100 and measurement apparatus 100A.

FIG. 7 is a flowchart showing a procedure of the measurement method withmeasurement apparatus 100 according to the present embodiment. Referringto FIG. 7, the user first powers on each component of the opticalcharacteristic measurement system and performs aging (step S100).Specifically, aging includes stabilization of the self-cooling functionof detection element 108 forming measurement apparatus 100,stabilization of the temperature in housing 102 of measurement apparatus100, stabilization of light source 4, and the like.

The user arranges a reference in integrator 6 such that the excitationlight from light source 4 is directly applied to the reference (stepS102). In the case of a powder sample or a solid sample, standardreflection member 69 (see FIG. 2B) serves as the reference. In the caseof a solution sample, only a solvent contained in a container of thesame type as that of a container containing the sample serves as thereference. Measurement apparatus 100 measures the light when theexcitation light is applied to the reference (step S104). Thismeasurement value is a value indicating an influence of light absorptionand the like that occur during measurement of the sample, and is used asa correction value.

Then, the user arranges a sample in integrator 6 such that theexcitation light from light source 4 is directly applied to the sample(step S106). Measurement apparatus 100 measures the light generated fromthe sample having received the excitation light (step S108). At thistime, measurement apparatus 100 measures the excitation light havingpassed through the sample and/or the excitation light having beenreflected by the sample, in addition to the light generated from thesample.

Then, the user makes a setting for correcting the re-excitationfluorescence (step S110). Measurement apparatus 100 measures the lightgenerated from the sample having received the excitation light (stepS112). As the setting for correcting the re-excitation fluorescence, inthe case of a powder sample or a solid sample, the sample is arranged ata position where the excitation light from light source 4 is notdirectly applied, and the light generated when the excitation lightreflected in integrator 6 is applied to the sample is measured. In thecase of a solution sample, measurement is performed in a state wherestandard reflection member 69 attached to sample window 65 of integrator6 is removed such that the excitation light having passed through thesample is not reflected in integrator 6.

Finally, by using the result of measurement by measurement apparatus 100in step S104, the result of measurement by measurement apparatus 100 instep S108, and the result of measurement by measurement apparatus 100 instep S112, data processing apparatus 200 calculates an opticalcharacteristic value (such as, for example, the quantum efficiency) ofthe sample (step S114).

G. Measurement Result Example

Next, one example of the result of measurement of the sample withoptical characteristic measurement system 1A shown in FIG. 6 will bedescribed. FIGS. 8A and 8B show an example of a measurement result whensinglet oxygen is generated from fullerene (C₆₀) in a solvent withoptical characteristic measurement system 1A shown in FIG. 6. FIG. 8Ashows, as Comparative Example, an example of using the measurementapparatus including the detection element whose detection sensitivity isset to be standard. FIG. 8B shows an example of employing theconfiguration shown in FIG. 4 and using the measurement apparatusincluding the detection element whose detection sensitivity is set to behigher.

More specifically, the excitation light was applied to fullereneexisting in a solvent of deuterated benzene (C₆D₆), to generate singletoxygen. FIG. 8 shows one example of a result of measurement of aspectrum of the fluorescence generated in the process of generatingsinglet oxygen. A 532 nm laser light source (output: 20 mW) was used aslight source 4 for generating the excitation light.

As shown in FIG. 8A, it can be seen that the spectrum of the generatedfluorescence cannot be measured when the detection sensitivity of thedetection element is set to be standard. On the other hand, as shown inFIG. 8B, it can be seen that the spectrum of the generated fluorescencecan be measured when the detection sensitivity of the detection elementis set to be higher.

Furthermore, by using optical characteristic measurement system 1A shownin FIG. 6, the internal quantum efficiency of fullerene in the solventwas measured. Correction of the re-excitation fluorescence was alsoperformed. In order to study the measurement stability, the samemeasurement was repeatedly performed on the same sample for 3 days (themeasurement was performed once a day and three times in total). Theresult is shown below.

-   -   First day: 0.061%    -   Second day: 0.062%    -   Third day: 0.062%

According to this result of measurement of the quantum efficiency, itcan be seen that the quantum efficiency can be measured in a stablemanner even in the case of the sample having very low quantumefficiency.

H. Calibration Method

Optical characteristic measurement system 1A shown in FIG. 6 includestwo measurement apparatuses 100 and 100A having different detectionsensitivities. With consideration given to measurement of the quantumefficiency and the like, energy calibration using the same standardlight source is required. That is to say, matching the size of energyconverted from the measurement value is required between the twomeasurement apparatuses. On the other hand, since the two measurementapparatuses have different detection sensitivities, energy calibrationabout the two measurement apparatuses using the same standard lightsource is not easy. Thus, one example of a calibration method formeasurement apparatuses 100 and 100A forming optical characteristicmeasurement system 1A according to the present embodiment will bedescribed.

FIG. 9 is a flowchart showing a procedure for performing calibration onoptical characteristic measurement system 1A according to the presentembodiment. FIGS. 10A to 10C are schematic views for describing theprocedure for performing calibration on optical characteristicmeasurement system 1A according to the present embodiment.

Referring to FIGS. 9 and 10A to 10C, a standard lamp 150 used forcalibration is first valued by an illumination and the like at adistance L1 with a preliminarily calibrated higher-order standard lightsource (an international standard traceable light source) (step S200). A50 W light source is, for example, used as standard lamp 150. By stepS200, an energy value for standard lamp 150 is obtained. The energyvalue is typically defined by using a spectral irradiance [μW cm⁻²nm⁻¹].

Then, standard lamp 150 which is a light source preliminarily valued bythe energy value and measurement apparatus 100A are arranged inaccordance with a prescribed arrangement condition. By way of example,as shown in FIG. 10A, standard lamp 150 and measurement apparatus 100A(standard sensitivity) are arranged, with optical axes thereof beingmatched with each other and with standard lamp 150 and measurementapparatus 100A being spaced apart from each other by distance L1 (stepS202). In order to reduce an influence of a stray light component andthe like generated from standard lamp 150, baffle units 152 and 154 arearranged between standard lamp 150 and measurement apparatus 100A.

An energy calibration coefficient of measurement apparatus 100A isdetermined based on an output value obtained by receiving the light fromstandard lamp 150 at measurement apparatus 100A. Namely, the energycalibration coefficient of measurement apparatus 100A is calculatedbased on the output value from measurement apparatus 100A under thearrangement condition shown in FIG. 10A (step S204).

The energy calibration coefficient is a coefficient for converting theoutput value (signal value) from the measurement apparatus into energy,and has a relationship of energy=output value after dark correction(measurement value−measurement value at the time of darkcorrection)/energy calibration coefficient.

In step S204, the energy calibration coefficient is calculated bysubtracting a dark correction value (a measurement value Id2 output in adark state) of measurement apparatus 100A from a measurement value I2 ofmeasurement apparatus 100A to obtain a value, and dividing this value bythe energy value valued to standard lamp 150. Namely, an energycalibration coefficient k2 of measurement apparatus 100A=(I2−Id2)/(anenergy value E1 valued to standard lamp 150).

Then, standard lamp 150 which is a light source and measurementapparatus 100A are arranged in accordance with a different arrangementcondition. By way of example, as shown in FIG. 10B, the distance betweenstandard lamp 150 and measurement apparatus 100A (standard sensitivity)is reduced from distance L1 to a distance L2, and a light attenuatingmesh 156 is arranged on the optical axis between standard lamp 150 andmeasurement apparatus 100A (step S206). A light attenuating mesh havinga transmittance of 1% (i.e., light attenuation to 1/100) can, forexample, be used as light attenuating mesh 156. A reason why thedistance is reduced from distance L1 to distance L2 is to reduce thedegree of light attenuation by light attenuating mesh 156, and changingthe distance is not necessary if more appropriate light attenuating mesh156 can be prepared.

A converted energy value of standard lamp 150 corresponding to thecurrent arrangement condition is determined based on the output valueobtained by receiving the light from standard lamp 150 at measurementapparatus 100A and the energy calibration coefficient of measurementapparatus 100A. Namely, the converted energy value of standard lamp 150reflecting light attenuating mesh 156 and distance L2 is calculatedbased on the output value from measurement apparatus 100A under thearrangement condition shown in FIG. 10B (step S208). Specifically, aconverted energy value E2 is calculated by subtracting the darkcorrection value (measurement value Id2 output in a dark state) ofmeasurement apparatus 100A from a measurement value I2′ of measurementapparatus 100A to obtain a value, and multiplying this value by energycalibration coefficient k2 calculated in step S204. Namely, convertedenergy value E2=(I2′−Id2)×energy calibration coefficient k2.

Then, standard lamp 150 which is a light source and measurementapparatus 100 are arranged in accordance with the different arrangementcondition. By way of example, with the arrangement state of baffle units152 and 154 and light attenuating mesh 156 being maintained in the stateshown in FIG. 10B, measurement apparatus 100 (higher sensitivity) isarranged instead of measurement apparatus 100A (standard sensitivity)(see FIG. 10C) (step S210).

An energy calibration coefficient of measurement apparatus 100 isdetermined based on an output value obtained by receiving the light fromstandard lamp 150 at measurement apparatus 100 and the converted energyvalue of standard lamp 150 corresponding to the arrangement condition inFIG. 10B. Namely, the energy calibration coefficient of measurementapparatus 100 is calculated based on the output value from measurementapparatus 100 under the arrangement condition shown in FIG. 10C (stepS212). In step S212, the energy calibration coefficient is calculated bysubtracting the dark correction value (a measurement value Id1 output ina dark state) of measurement apparatus 100 from a measurement value I1of measurement apparatus 100 to obtain a value, and dividing this valueby converted energy value E2 calculated in step S208. Namely, an energycalibration coefficient k1 of measurement apparatus100=(I1−Id1)/(converted energy value E2 of standard lamp 150).

In accordance with the procedure described above, the energy calibrationcoefficients of measurement apparatus 100 and measurement apparatus 100Acan be determined with the same standard light source.

In accordance with the difference in sensitivity between measurementapparatus 100 (higher sensitivity) and measurement apparatus 100A(standard sensitivity), a wattage of standard lamp 150, a differencebetween distance L1 and distance L2, the characteristics of the lightattenuating mesh, and the like may be adjusted appropriately.

I. Advantages

Measurement apparatus 100 according to the present embodiment has thefunction and configuration for suppressing the temperature variationsoccurring around detection element 108 in housing 102. With suchfunction and configuration, measurement with reduced influence ofmeasurement noise becomes possible even when the detection sensitivityof detection element 108 is increased. By using such measurementapparatus 100, the very feeble light generated from the sample when theexcitation light having a wavelength component in the ultraviolet regionor the visible region is applied to the sample can also be measured in astable manner, for example.

In addition, in measurement apparatus 100 according to the presentembodiment, the scheme for cooling detection element 108 itself and theinside of housing 102 with the electronic cooling element is employed.Therefore, the measurement time including aging can be significantlyshortened as compared with the scheme for cooling with liquid nitrogenor the like.

In optical characteristic measurement system 1A according to the presentembodiment, the light from the object to be measured can besimultaneously measured with measurement apparatus 100 and measurementapparatus 100A having different detection ranges. In both measurementapparatus 100 and measurement apparatus 100A, the array sensor (the CCDimage sensor as one example) is used as the detection element, andmeasurement apparatus 100 and measurement apparatus 100A can obtain theintensity of a plurality of wavelength components at a time. As aresult, the spectrum over the wide band can be measured with highersensitivity. In addition, the measurement time can be shortened ascompared with the wavelength sweeping scheme.

In addition, by optimizing the detection sensitivities of measurementapparatus 100 and measurement apparatus 100A, the very feeble light canbe measured in a stable manner with a high degree of reproducibility,without being affected by variations in ambient environment. Therefore,the quantum efficiency can be measured with a high degree of accuracy.With such an apparatus configuration, the fluorescence having awavelength component in the near-infrared region generated by asubstance in a living body can, for example, be detected. In addition,the present invention is also applicable to the development of variousmaterials. Furthermore, the present invention is also applicable to thefield of energy development in which the synthesized artificial light isused.

From the description above, the remaining advantages related to theoptical characteristic measurement apparatus and the opticalcharacteristic measurement system according to the present embodimentwill become clear.

While the embodiment of the present invention has been described, itshould be understood that the embodiment disclosed herein isillustrative and non-restrictive in every respect. The scope of thepresent invention is defined by the terms of the claims, and is intendedto include any modifications within the meaning and scope equivalent tothe terms of the claims.

What is claimed is:
 1. An optical characteristic measurement systemcomprising: a first measurement apparatus, the first measurementapparatus comprising: a first detection element arranged in a housing; afirst cooling unit at least partially joined to the first detectionelement, for cooling the first detection element; a suppressionmechanism for suppressing temperature variations occurring around thefirst detection element in the housing; and a first diffraction gratingarranged to correspond to the first detection element and configured toguide light in a first wavelength range to the first detection element;and a second measurement apparatus, the second measurement apparatuscomprising: a second detection element arranged in a housing; and asecond diffraction grating arranged to correspond to the seconddetection element and configured to guide light in a second wavelengthrange to the second detection element, wherein the first detectionelement of the first measurement apparatus is configured to have adetection sensitivity higher than a detection sensitivity of the seconddetection element of the second measurement apparatus.
 2. The opticalcharacteristic measurement system according to claim 1, furthercomprising a bifurcated fiber for bifurcating the light from an objectto be measured and guiding the light to each of the first and secondmeasurement apparatuses.
 3. The optical characteristic measurementsystem according to claim 1, wherein the first measurement apparatus isconfigured to have the detection sensitivity to a wavelength componentin a near-infrared region, and the second measurement apparatus isconfigured to have the detection sensitivity to at least a part ofwavelength components included in a range of an ultraviolet region to avisible region.
 4. A calibration method for an optical characteristicmeasurement system including a first measurement apparatus and a secondmeasurement apparatus configured to have a detection sensitivity lowerthan a detection sensitivity of the first measurement apparatus, themethod comprising: arranging a light source preliminarily valued by anenergy value and the second measurement apparatus in accordance with afirst arrangement condition, and determining an energy calibrationcoefficient of the second measurement apparatus based on an output valueobtained by receiving light from the light source at the secondmeasurement apparatus; arranging the light source and the secondmeasurement apparatus in accordance with a second arrangement condition,and determining a converted energy value of the light sourcecorresponding to the second arrangement condition based on the outputvalue obtained by receiving the light from the light source at thesecond measurement apparatus and the energy calibration coefficient ofthe second measurement apparatus; and arranging the light source and thefirst measurement apparatus in accordance with the second arrangementcondition, and determining an energy calibration coefficient of thefirst measurement apparatus based on an output value obtained byreceiving the light from the light source at the first measurementapparatus and the converted energy value of the light sourcecorresponding to the second arrangement condition.